1. Field of the Invention
The invention relates to an electromechanical storage cell based on alkali metal and chalcogen with at least one anode space to receive the anolyte and one cathode space to receive the catholyte. The spaces are separated from each other by a solid, alkali ion conducting electrolyte and bounded, at least zonewise, by a metallic housing. The solid electrolyte is designed in can shape and positively bonded at its open end, by a bonding material, to at least one ringshaped insulating part which limits the two reactant spaces relative to each other in the sealing zone of the storage cell closure.
2. Description of the Prior Art
Such rechargeable electrochemical storage cell with solid electrolytes are very well suited for the construction of storage batteries of high energy and power density. The solid electrolytes used in the alkali/chalcogen storage cells and made of beta aluminum oxide, for instance, are characterized in that the part conductivity of the moving ion is very high and the part conductivity of the electrons lower by many decimal powers. The use of such solid electrolytes for the construction of electrochemical storage cells achieves practically no self-discharge taking place because the conductivity of the electrons is negligible and the reaction substances cannot penetrate the solid electrolyte as neutral particles.
One specific example of such rechargeable electrochemical storage cells are those based on sodium and sulfur with a solid electrolyte made of beta aluminum oxide. One advantage of these electrochemical storage cells is that no secondary electrochemical reactions take place while charging. The reason for this is again that only one kind of ion can penetrate the solid electrolyte. Therefore, the current yield of such a sodium/sulfur storage cell is nearly 100%. Compared to the lead storage battery, the ratio of energy content to total weight of such a storage cell is very high in these electrochemical storage cells because the reacting substances are light and much energy is released in the electrochemical reaction. Thus, electrochemical storage cells on sodium and sulfur basis have considerable advantages over conventional storage batteries such as lead storage batteries.
Of disadvantage in these electrochemical storage cells is that they are kept at high operating temperatures of about 300.degree. to 500.degree.C. in order that required chemical reactions will proceed in the desired manner for charging and discharging. At these temperatures, considerable material problems are encountered. In particular, incompatibilities will develop between the structural materials used for the production of the storage cells and the reactants, especially the sodium and the sulfur. In the closure zone of this storage cell, where the openings of the reactant spaces meet, corrosion will occur despite the careful sealing of these spaces against each other. Until now, the elimination of corrosion has been insufficient.
An electrochemical storage cell in which the metallic storage cell housing is provided in its opening zone with a flange pointing inwardly is known from the German Published Non-Prosecuted Application DE-OS No. 2 556 279. This flange supports the solid electrolyte. The latter is provided with a flange pointing outwardly and resting against the metallic housing flange. The solid electrolyte flange is formed by a ringshaped insulating part fastened to the solid electrolyte tube by means of a special bonding material. The ringshaped insulating parts are preferably fastened on the outside to the open end of the solid electrolyte by means of a glass solder. Disposed between this insulating part and the metal housing flange on which it sits is a metallic gasket in the form of a dual-sided diamond edge washer. The opening of the solid electrolyte is closed by a metallic cover resting on the solid electrolyte flange. Another dual-sided diamond edge washer is disposed between the cover and the solid electrolyte flange.
U.S. Pat. No. 4,037,027 discloses an electrochemical storage cell in which the reactant spaces are sealed against each other and to the outside by the thermocompression method. It is by this method that the metallic housing parts are joined to the ceramic insulating ring of the solid electrolyte.
In these known solutions corrosion problems still persist inasmuch as the reaction substances of the reagents react chemically with the materials of the components located in the sealing zone. This causes corrosion products to develop with interfere with the electrochemical reactions or which corrode through the housing or the sealing elements of the electrochemical storage cell. With this, the tight seal between the reactant spaces on the one hand and of the entire storage cell towards the outside is lost. The glass used to bond the solid electrolyte tube to the insulating ring is particularly susceptible to corrosion. The glass is attacked by the sodium located in the interior of the can-shaped solid electrolyte in most electrochemical storage cell embodiments. The metallic housing of the storage cell, in turn, is subjected to corrosive actions by the sulfur and the sodium polysulfide which is formed, or by the vapors developing, especially in the sealing zone of the storage cell closure.